1. Field of the Invention
The present invention relates to shock absorbing components and to methods of manufacturing shock absorbing components. More particularly, the invention relates to flexible shock absorbing components used to provide cushioned surfaces or surface coverings.
2. Description of Related Art
There are many cushioning surfaces that have been used for athletic and recreational activities in indoor as well as outdoor facilities. For example, cushioned surfaces have been used for floor coverings or wall surfaces in indoor gymnasiums for indoor sports, as well as for home gyms and exercise mats. Examples of outdoor athletic and recreational areas where cushioned surfaces have been used to cover the ground include football fields, children""s playgrounds, and running tracks. Not only have cushioned surfaces been used for floor coverings and/or wall surfaces in athletic and recreational fields, but they also have been used in medical and health-related areas including nursing homes, hospitals and rehabilitation centers, and for animal enclosures to aid in animal comfort and safety.
There are three principle types of prior art cushioning structures used in flooring or wall surfaces for recreational use. First, there are cushioning structures that use solid materials such as rubber or rubber particles to provide the shock absorbing characteristics. A wearcourse is the term for outermost layer that comes into contact with the user and the elements. For example, wearcourses that have been used include rubber particle surfaces for tracks, nylon fibers and other materials used for synthetic grass.
Second, wood chips or sand have been used to provide cushioning of the ground surfaces in outdoor areas such as playgrounds to help reduce the impact from falls as a result of the activity, thereby reducing the risk of injury.
Third, mechanical means have been used to cushion the impacts. For example, one such mechanical means used in cushioned floor surfaces is vertical I beams. For example, the I-beam structure has been used in shock absorbing structures where honeycomb surfaces made from rubber provide support between the ground and the upper or outer surface. The I-beams in these structures are perpendicular to the surface.
Each of the three main types of prior art cushioning structures have certain disadvantages.
The first type of cushioned surface, made from solid materials such as rubber (i.e., foam rubber) or rubber particles, has the advantage of all weather use, but also has several disadvantages. The first disadvantage relates to the cost of manufacturing and adhering two layers of material together. Two layers are typically needed because the cushioning requirements are substantially different from the surface requirements. For example, in floor coverings, the bottom layer of material typically provides the cushioning features and the top layer of material provides comfort, traction and durability. The layers must have different structures and are manufactured from different materials having different characteristics.
A second disadvantage with prior art cushioned surfaces made from rubber or rubber particles is that they do not adequately cushion a fall. This is because the prior art cushioned structures made from rubber or rubber particles do not provide adequate impact management over the range of force exerted on the surface. For example, the impact absorption is not predictable throughout the surface and, especially at high impacts, the structures fail to provide sufficient cushioning.
A third disadvantage of prior art cushioning structures made from rubber or rubber particles is their lack of durability. In the past, many of these materials, such as foam rubber, used for the bottom layer of a two-layer cushioning structure lost their cushioning ability quickly and, failed to provide adequate cushioning for a sufficiently long period of time.
Wearcourse outdoor surfaces have additional disadvantages, primarily related to installation and durability. For example, wearcourse installation is tedious, labor intensive, and fraught with human error. Installation involves precise chemical mixing and handling of chemicals, often in less than optimum conditions or in the presence of children. Additionally, the range of colors available and customization is very limited. Lateral shock dispersion, which can reduce or prevent minor injuries such as broken fingers or skin abrasion, also is severely lacking.
As discussed above, the second type of cushioning surface is wood chips or sand, which typically have been used in outdoor areas such as playgrounds to provide cushioning. Although wood chips or sand are low cost alternatives, they also have disadvantages. One problem is that they do not provide uniformly adequate depth to provide adequate cushioning. For example, the loose particles move around so that the actual thickness of the cushioning layer varies significantly depending upon the level of usage and maintenance in a given area. Wood chips or sand fail to provide adequate cushioning for impacts where the loose fill particles do not have sufficient depth.
A second disadvantage with the loose fill materials is that the surface may not be solid enough to permit wheel chair access, especially where the loose fill material has substantial depth. Therefore, the use of wood chips or sand in outdoor recreational facilities may present a problem in satisfying the Americans with Disabilities Act access standards.
Mechanical cushioning structures in the prior art also have disadvantages. Although they may provide acceptable cushioning at low impacts, their cushioning ability is reduced at higher and more dangerous higher impacts. That is due to the tendency of prior art structure to buckle at high levels of impact. Specifically, we have found that prior art I-beam cushioning structures tend to buckle at a high level of impact, rendering this cushioning structure ineffective at some point during the impact.
This invention overcomes the above mentioned problems and disadvantages by providing a cushioning surface especially suited for recreational use, for both indoor and outdoor activities. The cushioning structure of the invention provides a surface having improved lateral shock dispersion, and improved impact protection. For example, the present invention provides superior impact protection for impacts due to falls of six feet or more onto the surface.
The invention provides a cushioning structure made of interconnected tiles that are fastened together to provide a continuous and smooth cushioning surface. Each tile is made from one or more sheets of thermoplastic material. In a preferred embodiment, two thermoplastic sheets are used. The thermoplastic material is preferably in the range of 0.005 to 0.100 inches, and most preferably about 0.050 inches. Thermoset elastomers or other thermoplastic rubber materials may be used for the sheets to handle larger temperature ranges.
Each sheet of thermoplastic material has a number of indentations therein, each indentation having a hemispherical or elliptical cross section. The hemispherical or elliptical shape of each indentation provides shock absorbing characteristics having a number of advantages in cushioning and durability. The indentations are made by thermoforming each sheet in a mold having hemispherical or elliptical protrusions. Each tile, after the indentations are thermoformed therein, will have a thickness of preferably about one inch in its non-compressed state. When two sheets are used, the thickness of a tile is preferably about two inches. In the two sheet configuration, indentations in each sheet face inwardly and may abut or be joined together. Two inches is preferred as the thickness, and it has been determined that a thickness of two inches will comply with ASTM playground standards. However, the thickness of the two sheets, when they are combined together, may be 12 inches or more in thickness.
One advantage of the present invention is that the top surface spreads the impact or load over a large cross sectional area of the cushioning layer. Another advantage of the present invention is that cushioning tiles may be manufactured and shipped at one location, and then installed at the desired site. Another advantage of the present invention is that the installation of the cushioning tiles requires far less labor than the prior art rubber or rubber particle cushioning structures. Another advantage of the present invention is that tiles having varied properties can be connected together at the installation site to accommodate different cushioning needs. For example, tiles having greater cushioning ability can be installed at equipment locations where risks are higher, while tiles having less impact protection can be installed in other lower risk areas.